The effects of urea infusion on glomerular filtration rate and renal plasma flow in sheep fed low and high protein diets.

Reducing the dietary N intake of sheep resulted in a significant fall in GFR with no change in RPF. Intravenous of urea for 19-46 h had no effect on the high protein diet but on the low protein diet GFR and FF were increased to values approaching those observed on the high protein diet. On the low protein diet GFR was unaffected by infusion of urea for 4 h or of saline alone for 30 h. It is suggested that the observed changes in GFR are associated with changes in the quantity of protein passing to the abomasum and small intestine.